Apparatus for applying developer powder to photo-conductive insulating sheets



Oct. 10, 1961 P. B. STREICH, SR 3,003,462

APPARATUS FOR APPLYING DEVELOPER POWDER TO PHOTO-CONDUCTIVE INSULATING SHEETS Filed Jan. 18, 1957 2 Sheets-Sheet l Q, mg INVENTOR PaaZ B.52Feich Sr.

Q BY m M ATTORNEY Oct. 10, 1961 P. B. STREICH, SR 3, 0 5

APPARATUS FOR APPLYING DEVELOPER POWDER TO PHOTO-CONDUCTIVE INSULATING SHEETS Filed Jan. 18. 1957 2 Sheets-Sheet 2 INVENTPR Paul BfiZfiezckSn ATTORNEY United States Patent 3,003,462 APPARATUS FOR APPLYING DEVELOPER POW- DER TO PHOTO-CONDUCTIVE INSULATENG SHEETS Paul B. Streich, Sr., Fox Lake, 111., assignor to Charles Bruning Company, Inc., Chicago, 111., a corporation of Delaware Filed Jan. 18, 1957, Scr. No. 634,373 1 Claim. (Cl. 118-637) This invention relates to apparatus for developing electrostatically charged latent images and more particularly to processes and apparatus for applying the developer powder or toner to electrostatically charged latent images on photo-conductive insulating sheets prior to the fixing of the developer powder to produce the desired prints.

Electrostatic printing techniques, as is well known, comprise producing a uniform electrostatic charge upon the surface of a photo-conductive insulating material, such, for example, as paper coated with a finely-divided photo-conductor, e.g., zinc oxide, applied to the paper base as a solution or suspension in a dielectric film-forming vehicle. The vehicle may be a resin solution or suspension, such as a solution of a silicone resin in a suitable solvent, or a suspension of a polyvinyl acetate resin in an aqueous medium. Further description of the photoconductive insulating material is believed unnecessary because the present invention may be used for applying developer powder to all known photo-conductive insulating materials.

The latent image is produced, as is also well known by exposing the charged surface to a light image, thus discharging the portions irradiated by the light rays while leaving the remainder of the surface in a charged condition. The latent image is then developed by applying a developer powder which is held electrostatically to the charged area. This powder is then fixed to the photoconductive surface, for example, by heat in those cases Where the powder is a resin or other material which can be fixed by heat, or by application of a solvent or by other known fixing technique.

It is well known to use a developer powder consisting essentially of a mixture of finely-divided magnetic carrier particles, such as finely-divided iron, magnetite or ferrites and developer powder such as the developer powders described, for example, in US. Patents 2,297,691, 2,618,552 and 2,638,416, including dyed or pigmented resin powders, e.g., Vinsol resin (treated pine resin) dyed with suitable dyes, coumarone-indene resins, gum copal, rosin, wax, etc.

The material for the developer powder and the magnetic material are selected in accordance with their triboelectric properties, so that when mixed the developer powder has the desired charge depending on the charge carried by the electrostatically charged latent image. Thus, in developing photo-conductive insulating material carrying a positively charged latent image, the developer powder should be so chosen that when mixed with the magnetic particles, it is negatively charged. Conversely, if the photo-conductive insulating material has a negatively charged latent image, the developer powder should be chosen so that when mixed with the magnetic particles, it carries a positive charge. Developer powder which when mixed with magnetic particles, such as iron, acquire the desired charges by triboelectric action are well known and can be selected from many materials that have been tested and occupy recognized positions in a triboelectric series. Thus, for example, pigmented rosin when mixed with iron becomes positively charged and can be used as the developer powder for developing negatively charged images. Colored Vinsol resin when mixed with iron becomes negatively charged and can be 3,003,462 Patented Oct. 10, 1961 ice used for developing positively charged images. As such mixtures containing developer powder and magnetic carrier particles are well known and per se do not form part of the present invention, further description thereof would serve no useful purpose.

Apparatus heretofore employed for applying the developer powder to the electrostatically charged latent images on photo-conductive insulating material frequently involve the formation of a cloud of developer powder which settles over the machine. This, of course, is objectionable, because not only does it result in an unpleas ant and unsightly working atmosphere, but also in the production of poor prints caused for example by developer particles from the cloud settling on the background areas.

It is among the objects of the present invention to provide an apparatus for applying developer powder to the electrostatically charged latent images on photo-conductive insulating sheets in which there is little or no tendency for the formation of a cloud of developer particles.

Another object of this invention is to provide such apparatus which result in uniform development of the images and with the production of images having a clear background.

()ther objects and advantages of this invention will be apparent from the following description thereof.

In the accompanying drawing forming a part of this specification and showing for purposes of exemplification a preferred form of this invention without limiting the claimed invention to such illustrative instance:

FIGURE 1 is a composite view partly in vertical section and partly in elevation and shows the developer powder applicator roll positioned in a trough containing a mixture of magnetic particles and developer powder and also shows a portion of the return feed screw disposed below the trough;

FlGURE 2 is a cross-section through the machine taken at right angles to the longitudinal axis of the applicator roll in a plane indicated by line 22 on FIGURE 1;

FIGURE 3 is a horizontal sectional view through the feed and return chambers and shows the applicator roll and the feed screws in the return and feed chambers in elevation; this figure, for the sake of clarity of illustration, shows the return or discharge chamber positioned laterally to one side of the applicator roll and not directly beneath the applicator roll as in FIGURES 1 and 2;

FlGURE 4 is a fragmentary plan view, showing the developer powder bin and its structural relationship to the applicator roll shown schematically in FIGURE 4;

FIGURE 5 is an end elevational view of the developer power bin taken in the directions indicated by arrows 5-5 on FlGURE 4 and illustrates one form of drive for the agitator and the return and feed screws; and

FlGURE 6 is a vertical section of the developer powder bin taken in a plane indicated by line 66 on FIGURE 4.

In the drawing, 10 indicates the frame of the machine on which is suitably fixed the trough 11. Suitably journaled for rotation, as for example, in ball bearings 12 mounted on frame ltl is the applicator roll 13. This roll, as best shown in FIGURE 1, is constituted of washer or disc-shaped magnets 14 mounted on a shaft 15 and alternating with washer or disc-shaped pole pieces 16 also mounted on shaft 15. The assembly of magnets 14 and pole pieces 16 are held on shaft 15 in face to face contact by nut 17 threaded on threaded end 13 of shaft 15. Each magnet 14 is magnetized throughout its thickness thus having an opposite pole on each face. Ideal magnets which are magnetized throughout their thickness suitable for use in this invention are those manufactured by the Indiana Steel Products Co., Valparaiso, Indiana, and sold under the trade name Lndox 1. The magnets 14 are assembled on shaft 15 with like poles of adjacent magnets facing each other but with the washer shaped ferrous pole pieces 16 separating them. The pole pieces are, therefore, alternately magnetized north and south along the length of the applicator roll. Thus, magnetic flux lines are formed extending throughout the periphery of-the'applicator roll 13; these flux lines are indicated at 19. 1

Applicator roll 13 has fixed to an extension of shaft 15 a driving sprocket which can be driven from any suitable source of power to rotate this roll with its periphery moving over a body 21 of magnetic particles and developer powder disposed in trough 11. The latter is formed with its upper edge or lip 22 positioned approximately of an inch from the periphery of the applicator roll 13, thus forming a narrow space between the periphery of this roll and the exit end of the trough which controls the thickness of the layer 23 on roll 13. Layer 23 is constituted of a mixture of developer powder and magnetic particles, which mixture is continuously brought up by the applicator roll 13 in its rotation, as clearly shown in FIGURE 2. 7

Trough I I is longitudinally elongated as shown in FIG- URE 3 and is provided near its base with anopening 24 disposed approximately midway between the ends of the trough 11. Communicating with this opening 24 is a feed chamber 25 having rotatably mounted in its base a feed screw 26. End 27 of chamber 25 remote from opening 24 communicates with one end of a bin 28. Bin 28 also communicates with a longitudinally extending discharge chamber 29 provided with openings 31 and 32 communicably connecting the discharge chamber 29 with the opposite ends of the trough 11. Disposed in the base of 9 the discharge chamber 29 is a feed screw 33 which is mounted for rotation in the base of the discharge chamber and extends the length thereof. Rotation of the feed screws 26 and 29 can be effected, for example, by a chain drive involvinga chain 34 passing over sprockets on the applicator roll shaft and the shaft of feed screw 33 and a second chain 35 passing over sprockets 36 fixed to the shafts of feed screws 33 and 26. It will be understood other suitable drives may be used. 7

Mounted for rotation on a shaft 37 in bin 28 is an agitator 38. In the embodiment of the invention shown in FIGURES 3, 4 and 6 the agitator is in the form of a rotating hub 39 having radially extending'arms 41. This agitator may be rotated by the drive chain 35 which drives the sprocket 42 fixed to its shaft 37. In its rotation it not only eifects agitation of the developer powder magnetic particles mixture but also elevates the mixture along the upwardly rising wall 43 (FIGURE 5) of bin 28 to deliver the mixture to the feed chamber 26.

Feeding of the photo-conductive insulating material 45, as shown in FIGURE 2, is effected by two sets of feed rollers 46 and 47 suitably spaced on opposite sides of the applicator roll 13, and which feed the insulating material 45 into tangential contact with layer 23 on roll 13. These feed rollers may have their peripheries of nap or pile material to provide a soft, firm drive for the insulating material 45. The nap or pile material is of a material in the triboelectric series which is located in this series remote from the position in the series of the material of which the developer powder is constiuted. Thus, if the developer power carries a positive charge, the nap may be of Orlon, Dacron, Saran fiber, or acetate rayon. If it has a negative charge, it may be of nylon, glass W001, W001 or animal fur. Such feed rolls are more completely described in the copending patent application of John I. Schulze, Serial No. 629,069 (now Patent No. 2,894,744

Mounted for rotation directly above the applicator roll 16 are a pair of spaced polygonal agitating rolls 48 and 49, positioned so that their peripheries engage the back of insulating material 45 as it is fed over the applicator roll 13. While in the embodiment shown in FIG- URE 2 these rollers are shown hexagonal in shape, they may be rectangular or other polygonal shape. These rollers are driven from any suitable drive at a relatively 4 rapid rate, e.g., from 1,000 to 2,000 rpm. to rapidly vibrate or agitate the sheet of insulating material 45 passing face down over the applicator roll [13.

In operation, the applicator roll 13 is rotated in the direction of the arrows on FIGURE 2. The mixture of developer powder and magnetic particles is fed by feed screw 26 to the opening 24. This mixture is attracted by the magnetic fields at the periphery of the pole pieces and is pulled through the opening 2 4. This action produces the layer 23 of magnetic particles and developer powder mixture on the surface of the roll of even thickness determined by the space between the periphery of the applicator roll 13 and the lip 22 of trough 11.

When a charged and exposed sheet or web 45 of photoconductive insulating material is passed over the applicator roll 13, as shown in FIGURE 2, the developer powder is attracted to the charged image thereon. The magnetic particles and unused developer powder are held on the applicator roll and as indicated at 51 revolve with this roll into the mixture of developer powder and magnetic particles in trough 11. As the roll 13 rotates over the mixture of developer powder and magnetic particles continuously circulated through the trough 11, the developer powder on the applicator roll 13 is replen shed because of the triboelectric attraction between the magnetic particles and the developer powder. Hence, the roll 13 as it moves up into contact with insulating material 45 again presents a smooth, fresh, uniform mixture of magnetic particles and developer powder as it passes the lip 22.

Trough 11 is at ground potential which maintains the natural charge on both the magnetic particles and the developer powder in the layer'23 of this mixture on the applicator roll 13 applied to the photo-conductive insulat ing material 45. The electrostatic charge on the insulating material 45 has a greater attraction for the developer power'than the magnetic particles have and, hence, the developer powder adheres to the image. In the passage of the insulating material through the conventional fixing apparatus, the developer powder is fixed to produce the desired prints.

The polygonal rolls 48 and 49 are driven preferably by means of a timing belt in timed relation with'the speed of movement of the applicator roll. Rolls 48 and,

49 vibrate the photo-conductive insulating material 45 against the applicator roll 13. This agitates the mixture of magnetic particles and developer powder and forces them to cover the image uniformly and completely. 5

Best results are obtained by rapid vibration of the im sulating material 45 because the electrostatic field is small and willattract the developer powder only a minute distance. Rapid vibration of the insulating material 45 effected, for example, by rotating rolls 48 and 49 at a speed of from 1000 to 2000 rpm. gives optimum coverage of' the image with the developer powder.

The direction of flow of the mixture of magnetic particles and developer powder through the apparatus is shown by the arrows on FIGURE 3. After the mixture enters the opening 24, it spreads under the applicator roll 13 for the full length of this roll and exits from the trough 1i through'the openings 31 and 32 at the opposite ends thereof into the discharge chamber 29.. From this chamber 29, discharge screw 33 feeds the mixture into bin 28 where the mixture is agitated by agitator 38 and elevated thereby into the feed'chamber 25. Feed screw 26 feeds the mixture through chamber 25 to the inlet opening 24 of the trough 11.

The magnetic particles mix with the developer powder as the mixture moves and this mixture as it passes under roll 13 continuously reforms the layer 23 thereon. As developer powder is depleted, it is readily replenished by placing more in the bin 28, where it combines with the mixture passing therethrough under the influence of the agitator 38 and the circulating stream of the mixture.

Preferably, the applicator roll 13 is driven at the same surface sp ed, as the insulating material 45. This cums nates any tendency to form a cloud of developer powder that would settle over the machine. The agitating rolls 48 and 49 do not come into contact with the developer powder and, hence, do not cause the formation of such objectionable cloud.

It will be noted that a relatively large quantity of magnetic particles and developer powder can be maintained in circulation through the apparatus as hereinabove described. Hence, it is not necessary to replenish the developer powder except at infrequent intervals. The constant agitation of the developer powder caused by the flow thereof, as hereinabove described, results in even development of the prints. Moreover, as the insulating material is run face down over the applicator roll 13, any developer powder that would tend to stick to the background is jolted loose from the insulating material by the rolls 48 and 49 and falls back onto the applicator roll. Hence, images with especially clean backgrounds result.

The present invention is ideally suited for developing sheets or webs of insulating material because the applicator roll 13 and the feed rolls 46 and 47 can be driven at the same surface speed.

The parts of the machine may be of any suitable materials of construction which will not deleteriously aifect the magnetic field surrounding the periphery of the applicator roll 13 and the magnetic attraction between the roll and the developer powder mixture and between the image on the photo conductive insulating material and the developer powder. Thus frame and the drive sprockets may be of steel, the pole pieces of ferrous metal, shaft of non-ferrous metal such as brass or aluminum, trough 11 and feed screws 26 and 33 of non-ferrous material such as brass, aluminum or plastic, nut 17 of non-ferrous metal such as brass or aluminum and the packing 52 about this nut 17 of felt, plastic or other non-magnetic material. Packing 51 serves as a seal for the end of the applicator roll 13 to prevent loss of developer powder mixture, and being non-magnetic allows the developer powder mixture to leave the ends of the applicator roll and be deposited in the discharge chamber 29.

Since certain changes in the developer set forth, which embody the invention, may be made without departing from its scope, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

Apparatus for developing electrostatically charged latent images on photo-conductive insulating sheets comprising, in combination, means for moving said photoconductive insulating sheets in a substantially horizontal plane, a container for a body of developer mixture consisting essentially of magnetic particles and developer powder, a cylindrical applicator mounted in said container with the periphery of said cylindrical applicator arranged to move through the upper portion of said body of developer mixture, the Width of said cylindrical applicator being at least equal to the transverse extent of the entire image areas on said photo-conductive insulating sheets, said cylindrical applicator being positioned to have said photo-conductive insulating sheets pass in substantially tangential contact with the upper periphery thereof with the direction of movement of said photo-conductive insulating sheets in said horizontal plane being the same as the direction of rotation of said cylindrical applicator,

.eans for creating a magnetic field in the periphery of said cylindrical applicator and to form thereon during its rotation a layer of magnetic particles and developer powder having a transverse extent at least equal to the complete width of the entire image areas on said photoconductive insulating sheets which layer is continuous and unbroken throughout said transverse extent and is also continuous and unbroken in the direction of rotation of said cylindrical applicator from the upper surface of said body to the point of application of the developer powder to the photo-conductive insulating sheets, and means for rotating said cylindrical applicator to bring said layer into substantially tangential contact with said moving photo-conductive insulating sheets with both said layer and said insulating sheets in the area of substantially tangential contact moving in the same general direction to thus apply developer powder from said layer onto said photo-conductive insulating sheets across the entire transverse extent of the image areas thereon, said means for creating a magnetic field in the surface of said cylindrical applicator and for rotating said cylindrical applicator efiecting replenishing of the devolper powder in said layer upon rotation of said cylindrical applicator through the upper portion of the body of developer powder to reform said layer for application of developer powder therein to successive photo-conductive insulating sheets.

References Cited in the file of this patent UNITED STATES PATENTS 668,941 Waring Feb. 26, 1901 1,114,071 Ullrich Oct. 20, 1914 2,376,922 King May 29, 1945 2,625,905 Richards Jan. 20, 1953 2,686,733 Burridge et al. Aug. 17, 1954 2,763,204 Sims Sept. 18, 1956 2,786,440 Giaimo Mar. 26, 1957 2,786,441 Young Mar. 26, 1957 2,791,949 Simmons et al May 14, 1957 2,811,465 Greig Oct. 29, 1957 2,822,779 Schroeder Feb. 11, 1958 2,841,461 Gleason July 1, 1958 2,854,947 Giaimo Oct. 7, 1958 

